FreeBSD Manual Pages

LOADER(8) FreeBSD System Manager's Manual LOADER(8)
NAMEloader -- kernel bootstrapping final stage
DESCRIPTION
The program called loader is the final stage of FreeBSD's kernel boot-
strapping process. On IA32 (i386) architectures, it is a BTX client. It
is linked statically to libstand(3) and usually located in the directory
/boot.
It provides a scripting language that can be used to automate tasks, do
pre-configuration or assist in recovery procedures. This scripting lan-
guage is roughly divided in two main components. The smaller one is a
set of commands designed for direct use by the casual user, called
"builtin commands" for historical reasons. The main drive behind these
commands is user-friendliness. The bigger component is an ANS Forth com-
patible Forth interpreter based on FICL, by John Sadler.
During initialization, loader will probe for a console and set the
console variable, or set it to serial console (``comconsole'') if the
previous boot stage used that. If multiple consoles are selected, they
will be listed separated by spaces. Then, devices are probed, currdev
and loaddev are set, and LINES is set to 24. Next, FICL is initialized,
the builtin words are added to its vocabulary, and /boot/boot.4th is pro-
cessed if it exists. No disk switching is possible while that file is
being read. The inner interpreter loader will use with FICL is then set
to interpret, which is FICL's default. After that, /boot/loader.rc is
processed if available, and, failing that, /boot/boot.conf is read for
historical reasons. These files are processed through the include com-
mand, which reads all of them into memory before processing them, making
disk changes possible.
At this point, if an autoboot has not been tried, and if autoboot_delay
is not set to ``NO'' (not case sensitive), then an autoboot will be
tried. If the system gets past this point, prompt will be set and loader
will engage interactive mode. Please note that historically even when
autoboot_delay is set to ``0'' user will be able to interrupt autoboot
process by pressing some key on the console while kernel and modules are
being loaded. In some cases such behaviour may be undesirable, to pre-
vent it set autoboot_delay to ``-1'', in this case loader will engage
interactive mode only if autoboot has failed.
BUILTIN COMMANDS
In loader, builtin commands take parameters from the command line.
Presently, the only way to call them from a script is by using evaluate
on a string. If an error condition occurs, an exception will be gener-
ated, which can be intercepted using ANS Forth exception handling words.
If not intercepted, an error message will be displayed and the inter-
preter's state will be reset, emptying the stack and restoring interpret-
ing mode.
The builtin commands available are:
autoboot [seconds [prompt]]
Proceeds to bootstrap the system after a number of seconds, if
not interrupted by the user. Displays a countdown prompt warning
the user the system is about to be booted, unless interrupted by
a key press. The kernel will be loaded first if necessary.
Defaults to 10 seconds.
bcachestat
Displays statistics about disk cache usage. For debugging only.
bootbootkernelname [...]
boot-flag...
Immediately proceeds to bootstrap the system, loading the kernel
if necessary. Any flags or arguments are passed to the kernel,
but they must precede the kernel name, if a kernel name is pro-
vided.
WARNING: The behavior of this builtin is changed if loader.4th(8)
is loaded.
echo [-n] [<message>]
Displays text on the screen. A new line will be printed unless
-n is specified.
heap Displays memory usage statistics. For debugging purposes only.
help [topic [subtopic]]
Shows help messages read from /boot/loader.help. The special
topic index will list the topics available.
includefile [file...]
Process script files. Each file, in turn, is completely read
into memory, and then each of its lines is passed to the command
line interpreter. If any error is returned by the interpreter,
the include command aborts immediately, without reading any other
files, and returns an error itself (see ERRORS).
load [-ttype] file...
Loads a kernel, kernel loadable module (kld), or file of opaque
contents tagged as being of the type type. Kernel and modules
can be either in a.out or ELF format. Any arguments passed after
the name of the file to be loaded will be passed as arguments to
that file. Currently, argument passing does not work for the
kernel.
load_geli [-nkeyno] provfile
Loads a geli(8) encryption keyfile for the given provider name.
The key index can be specified via keyno or will default to zero.
ls [-l] [path]
Displays a listing of files in the directory path, or the root
directory if path is not specified. If -l is specified, file
sizes will be shown too.
lsdev [-v]
Lists all of the devices from which it may be possible to load
modules. If -v is specified, more details are printed.
lsmod [-v]
Displays loaded modules. If -v is specified, more details are
shown.
morefile [file...]
Display the files specified, with a pause at each LINES dis-
played.
pnpscan [-v]
Scans for Plug-and-Play devices. This is not functional at
present.
read [-tseconds] [-pprompt] [variable]
Reads a line of input from the terminal, storing it in variable
if specified. A timeout can be specified with -t, though it will
be canceled at the first key pressed. A prompt may also be dis-
played through the -p flag.
reboot Immediately reboots the system.
setvariablesetvariable=value
Set loader's environment variables.
show [variable]
Displays the specified variable's value, or all variables and
their values if variable is not specified.
unload Remove all modules from memory.
unsetvariable
Removes variable from the environment.
? Lists available commands.
BUILTINENVIRONMENTVARIABLES
The loader has actually two different kinds of `environment' variables.
There are ANS Forth's environmentalqueries, and a separate space of
environment variables used by builtins, which are not directly available
to Forth words. It is the latter type that this section covers.
Environment variables can be set and unset through the set and unset
builtins, and can have their values interactively examined through the
use of the show builtin. Their values can also be accessed as described
in BUILTINPARSER.
Notice that these environment variables are not inherited by any shell
after the system has been booted.
A few variables are set automatically by loader. Others can affect the
behavior of either loader or the kernel at boot. Some options may
require a value, while others define behavior just by being set. Both
types of builtin variables are described below.
autoboot_delay
Number of seconds autoboot will wait before booting. If this
variable is not defined, autoboot will default to 10 seconds.
If set to ``NO'', no autoboot will be automatically attempted
after processing /boot/loader.rc, though explicit autoboot's
will be processed normally, defaulting to 10 seconds delay.
If set to ``0'', no delay will be inserted, but user still will
be able to interrupt autoboot process and escape into the
interactive mode by pressing some key on the console while ker-
nel and modules are being loaded.
If set to ``-1'', no delay will be inserted and loader will
engage interactive mode only if autoboot has failed for some
reason.
boot_askname
Instructs the kernel to prompt the user for the name of the
root device when the kernel is booted.
boot_cdrom
Instructs the kernel to try to mount the root file system from
CD-ROM.
boot_ddb Instructs the kernel to start in the DDB debugger, rather than
proceeding to initialize when booted.
boot_dfltroot
Instructs the kernel to mount the statically compiled-in root
file system.
boot_gdb Selects gdb-remote mode for the kernel debugger by default.
boot_multicons
Enables multiple console support in the kernel early on boot.
In a running system, console configuration can be manipulated
by the conscontrol(8) utility.
boot_mute
All console output is suppressed when console is muted. In a
running system, the state of console muting can be manipulated
by the conscontrol(8) utility.
boot_pause
During the device probe, pause after each line is printed.
boot_serial
Force the use of a serial console even when an internal console
is present.
boot_single
Prevents the kernel from initiating a multi-user startup;
instead, a single-user mode will be entered when the kernel has
finished device probing.
boot_verbose
Setting this variable causes extra debugging information to be
printed by the kernel during the boot phase.
bootfile List of semicolon-separated search path for bootable kernels.
The default is ``kernel''.
comconsole_speed
Defines the speed of the serial console (i386 and amd64 only).
If the previous boot stage indicated that a serial console is
in use then this variable is initialized to the current speed
of the console serial port. Otherwise it is set to 9600 unless
this was overridden using the BOOT_COMCONSOLE_SPEED variable
when loader was compiled. Changes to the comconsole_speed
variable take effect immediately.
comconsole_port
Defines the base i/o port used to access console UART (i386 and
amd64 only). If the variable is not set, its assumed value is
0x3F8, which corresponds to PC port COM1, unless overridden by
BOOT_COMCONSOLE_PORT variable during the compilation of loader.
Setting the comconsole_port variable automatically set
hw.uart.console environment variable to provide a hint to ker-
nel for location of the console. Loader console is changed
immediately after variable comconsole_port is set.
comconsole_pcidev
Defines the location of a PCI device of the 'simple communica-
tion' class to be used as the serial console UART (i386 and
amd64 only). The syntax of the variable is
'bus:device:function[:bar]', where all members must be numeric,
with possible 0x prefix to indicate a hexadecimal value. The
bar member is optional and assumed to be 0x10 if omitted. The
bar must decode i/o space. Setting the variable
comconsole_pcidev automatically sets the variable
comconsole_port to the base of the selected bar, and hint
hw.uart.console. Loader console is changed immediately after
variable comconsole_pcidev is set.
console Defines the current console or consoles. Multiple consoles may
be specified. In that case, the first listed console will
become the default console for userland output (e.g. from
init(8)).
currdev Selects the default device. Syntax for devices is odd.
init_chroot
If set to a valid directory in the root file system, it causes
init(8) to perform a chroot(2) operation on that directory,
making it the new root directory. That happens before entering
single-user mode or multi-user mode (but after executing the
init_script if enabled).
init_path
Sets the list of binaries which the kernel will try to run as
the initial process. The first matching binary is used. The
default list is ``/sbin/init:/sbin/oinit:/sbin/init.bak:
/rescue/init:/stand/sysinstall''.
init_script
If set to a valid file name in the root file system, instructs
init(8) to run that script as the very first action, before
doing anything else. Signal handling and exit code interpreta-
tion is similar to running the /etc/rc script. In particular,
single-user operation is enforced if the script terminates with
a non-zero exit code, or if a SIGTERM is delivered to the
init(8) process (PID 1).
init_shell
Defines the shell binary to be used for executing the various
shell scripts. The default is ``/bin/sh''. It is used for
running the init_script if set, as well as for the /etc/rc and
/etc/rc.shutdown scripts. The value of the corresponding
kenv(2) variable is evaluated every time init(8) calls a shell
script, so it can be changed later on using the kenv(1) util-
ity. In particular, if a non-default shell is used for running
an init_script, it might be desirable to have that script reset
the value of init_shell back to the default, so that the
/etc/rc script is executed with the standard shell /bin/sh.
interpret
Has the value ``OK'' if the Forth's current state is interpret-
ing.
LINES Define the number of lines on the screen, to be used by the
pager.
module_path
Sets the list of directories which will be searched for modules
named in a load command or implicitly required by a dependency.
The default value for this variable is
``/boot/kernel;/boot/modules''.
num_ide_disks
Sets the number of IDE disks as a workaround for some problems
in finding the root disk at boot. This has been deprecated in
favor of root_disk_unit.
prompt Value of loader's prompt. Defaults to ``${interpret}''. If
variable prompt is unset, the default prompt is `>'.
root_disk_unit
If the code which detects the disk unit number for the root
disk is confused, e.g. by a mix of SCSI and IDE disks, or IDE
disks with gaps in the sequence (e.g. no primary slave), the
unit number can be forced by setting this variable.
rootdev By default the value of currdev is used to set the root file
system when the kernel is booted. This can be overridden by
setting rootdev explicitly.
Other variables are used to override kernel tunable parameters. The fol-
lowing tunables are available:
hw.physmem Limit the amount of physical memory the system will use.
By default the size is in bytes, but the k, K, m, M, g and
G suffixes are also accepted and indicate kilobytes,
megabytes and gigabytes respectively. An invalid suffix
will result in the variable being ignored by the kernel.
hw.pci.host_start_mem, hw.acpi.host_start_mem
When not otherwise constrained, this limits the memory
start address. The default is 0x80000000 and should be set
to at least size of the memory and not conflict with other
resources. Typically, only systems without PCI bridges
need to set this variable since PCI bridges typically con-
strain the memory starting address (and the variable is
only used when bridges do not constrain this address).
hw.pci.enable_io_modes
Enable PCI resources which are left off by some BIOSes or
are not enabled correctly by the device driver. Tunable
value set to ON (1) by default, but this may cause problems
with some peripherals.
kern.maxusers
Set the size of a number of statically allocated system
tables; see tuning(7) for a description of how to select an
appropriate value for this tunable. When set, this tunable
replaces the value declared in the kernel compile-time con-
figuration file.
kern.ipc.nmbclusters
Set the number of mbuf clusters to be allocated. The value
cannot be set below the default determined when the kernel
was compiled.
kern.ipc.nsfbufs
Set the number of sendfile(2) buffers to be allocated.
Overrides NSFBUFS. Not all architectures use such buffers;
see sendfile(2) for details.
kern.maxswzone
Limits the amount of KVM to be used to hold swap metadata,
which directly governs the maximum amount of swap the sys-
tem can support, at the rate of approximately 200 MB of
swap space per 1 MB of metadata. This value is specified
in bytes of KVA space. If no value is provided, the system
allocates enough memory to handle an amount of swap that
corresponds to eight times the amount of physical memory
present in the system.
Note that swap metadata can be fragmented, which means that
the system can run out of space before it reaches the theo-
retical limit. Therefore, care should be taken to not con-
figure more swap than approximately half of the theoretical
maximum.
Running out of space for swap metadata can leave the system
in an unrecoverable state. Therefore, you should only
change this parameter if you need to greatly extend the KVM
reservation for other resources such as the buffer cache or
kern.ipc.nmbclusters. Modifies kernel option
VM_SWZONE_SIZE_MAX.
kern.maxbcache
Limits the amount of KVM reserved for use by the buffer
cache, specified in bytes. The default maximum is 200MB on
i386, and 400MB on amd64 and sparc64. This parameter is
used to prevent the buffer cache from eating too much KVM
in large-memory machine configurations. Only mess around
with this parameter if you need to greatly extend the KVM
reservation for other resources such as the swap zone or
kern.ipc.nmbclusters. Note that the NBUF parameter will
override this limit. Modifies VM_BCACHE_SIZE_MAX.
kern.msgbufsize
Sets the size of the kernel message buffer. The default
limit of 64KB is usually sufficient unless large amounts of
trace data need to be collected between opportunities to
examine the buffer or dump it to a file. Overrides kernel
option MSGBUF_SIZE.
machdep.disable_mtrrs
Disable the use of i686 MTRRs (x86 only).
net.inet.tcp.tcbhashsize
Overrides the compile-time set value of TCBHASHSIZE or the
preset default of 512. Must be a power of 2.
vm.kmem_size Sets the size of kernel memory (bytes). This overrides the
value determined when the kernel was compiled. Modifies
VM_KMEM_SIZE.
vm.kmem_size_minvm.kmem_size_max
Sets the minimum and maximum (respectively) amount of ker-
nel memory that will be automatically allocated by the ker-
nel. These override the values determined when the kernel
was compiled. Modifies VM_KMEM_SIZE_MIN and
VM_KMEM_SIZE_MAX.
BUILTINPARSER
When a builtin command is executed, the rest of the line is taken by it
as arguments, and it is processed by a special parser which is not used
for regular Forth commands.
This special parser applies the following rules to the parsed text:
1. All backslash characters are preprocessed.
+o \b , \f , \r , \n and \t are processed as in C.
+o \s is converted to a space.
+o \v is converted to ASCII 11.
+o \z is just skipped. Useful for things like ``\0xf\z\0xf''.
+o \0xN and \0xNN are replaced by the hex N or NN.
+o \NNN is replaced by the octal NNN ASCII character.
+o \" , \' and \$ will escape these characters, preventing them
from receiving special treatment in Step 2, described below.
+o \\ will be replaced with a single \ .
+o In any other occurrence, backslash will just be removed.
2. Every string between non-escaped quotes or double-quotes will be
treated as a single word for the purposes of the remaining steps.
3. Replace any $VARIABLE or ${VARIABLE} with the value of the environ-
ment variable VARIABLE.
4. Space-delimited arguments are passed to the called builtin command.
Spaces can also be escaped through the use of \\ .
An exception to this parsing rule exists, and is described in BUILTINSANDFORTH.
BUILTINSANDFORTH
All builtin words are state-smart, immediate words. If interpreted, they
behave exactly as described previously. If they are compiled, though,
they extract their arguments from the stack instead of the command line.
If compiled, the builtin words expect to find, at execution time, the
following parameters on the stack:
addrNlenN...addr2len2addr1len1N
where addrXlenX are strings which will compose the command line that
will be parsed into the builtin's arguments. Internally, these strings
are concatenated in from 1 to N, with a space put between each one.
If no arguments are passed, a 0 must be passed, even if the builtin
accepts no arguments.
While this behavior has benefits, it has its trade-offs. If the execu-
tion token of a builtin is acquired (through ' or [']), and then passed
to catch or execute, the builtin behavior will depend on the system state
atthetimecatchorexecuteisprocessed! This is particularly annoying
for programs that want or need to handle exceptions. In this case, the
use of a proxy is recommended. For example:
: (boot) boot;
FICL
FICL is a Forth interpreter written in C, in the form of a forth virtual
machine library that can be called by C functions and vice versa.
In loader, each line read interactively is then fed to FICL, which may
call loader back to execute the builtin words. The builtin include will
also feed FICL, one line at a time.
The words available to FICL can be classified into four groups. The ANS
Forth standard words, extra FICL words, extra FreeBSD words, and the
builtin commands; the latter were already described. The ANS Forth stan-
dard words are listed in the STANDARDS section. The words falling in the
two other groups are described in the following subsections.
FICLEXTRAWORDS.env.ver-roll2constant
>namebody>
compare This is the STRING word set's compare.
compile-onlyendifforget-widparse-wordsliteral This is the STRING word set's sliteral.
wid-set-superw@w!x.emptycell--rotFREEBSDEXTRAWORDS$ (--) Evaluates the remainder of the input buffer, after having
printed it first.
% (--) Evaluates the remainder of the input buffer under a catch
exception guard.
.# Works like . but without outputting a trailing space.
fclose (fd--)
Closes a file.
fkey (fd--char)
Reads a single character from a file.
fload (fd--)
Processes a file fd.
fopen (addrlenmode -- fd)
Opens a file. Returns a file descriptor, or -1 in case of
failure. The mode parameter selects whether the file is to be
opened for read access, write access, or both. The constants
O_RDONLY, O_WRONLY, and O_RDWR are defined in
/boot/support.4th, indicating read only, write only, and read-
write access, respectively.
fread (fdaddrlen--len')
Tries to read len bytes from file fd into buffer addr. Returns
the actual number of bytes read, or -1 in case of error or end
of file.
heap? (-- cells)
Return the space remaining in the dictionary heap, in cells.
This is not related to the heap used by dynamic memory alloca-
tion words.
inb (port--char)
Reads a byte from a port.
key (-- char)
Reads a single character from the console.
key? (-- flag)
Returns true if there is a character available to be read from
the console.
ms (u--)
Waits u microseconds.
outb (portchar--)
Writes a byte to a port.
seconds (-- u)
Returns the number of seconds since midnight.
tib> (-- addrlen)
Returns the remainder of the input buffer as a string on the
stack.
trace! (flag--)
Activates or deactivates tracing. Does not work with catch.
FREEBSDDEFINEDENVIRONMENTALQUERIES
arch-i386
TRUE if the architecture is IA32.
FreeBSD_version
FreeBSD version at compile time.
loader_version
loader version.
SYSTEMDOCUMENTATIONFILES
/boot/loader loader itself.
/boot/boot.4th Additional FICL initialization.
/boot/boot.conf loader bootstrapping script. Deprecated.
/boot/defaults/loader.conf
/boot/loader.conf
/boot/loader.conf.local loader configuration files, as described in
loader.conf(5).
/boot/loader.rc loader bootstrapping script.
/boot/loader.help Loaded by help. Contains the help messages.
EXAMPLES
Boot in single user mode:
boot -s
Load the kernel, a splash screen, and then autoboot in five seconds.
Notice that a kernel must be loaded before any other load command is
attempted.
load kernel
load splash_bmp
load -t splash_image_data /boot/chuckrulez.bmp
autoboot 5
Set the disk unit of the root device to 2, and then boot. This would be
needed in a system with two IDE disks, with the second IDE disk hardwired
to ada2 instead of ada1.
set root_disk_unit=2
boot /boot/kernel/kernel
See also:
/boot/loader.4th Extra builtin-like words.
/boot/support.4thloader.conf processing words.
/usr/share/examples/bootforth/ Assorted examples.
ERRORS
The following values are thrown by loader:
100 Any type of error in the processing of a builtin.
-1 Abort executed.
-2 Abort" executed.
-56 Quit executed.
-256 Out of interpreting text.
-257 Need more text to succeed -- will finish on next run.
-258 Bye executed.
-259 Unspecified error.
SEE ALSOlibstand(3), loader.conf(5), tuning(7), boot(8), btxld(8)STANDARDS
For the purposes of ANS Forth compliance, loader is an ANSForthSystemwithEnvironmentalRestrictions,Providing .(, :noname, ?do, parse, pick,
roll, refill, to, value, \, false, true, <>, 0<>, compile, , erase, nip,
tuck and marker fromtheCoreExtensionswordset,ProvidingtheExcep-tionExtensionswordset,ProvidingtheLocalsExtensionswordset,Pro-vidingtheMemory-AllocationExtensionswordset,Providing .s, bye, for-
get, see, words, [if], [else] and [then] fromtheProgramming-Toolsextensionwordset,ProvidingtheSearch-Orderextensionswordset.HISTORY
The loader first appeared in FreeBSD 3.1.
AUTHORS
The loader was written by Michael Smith <msmith@FreeBSD.org>.
FICL was written by John Sadler <john_sadler@alum.mit.edu>.
BUGS
The expect and accept words will read from the input buffer instead of
the console. The latter will be fixed, but the former will not.
FreeBSD 9.3 October 1, 2013 FreeBSD 9.3